This invention relates to a running web cutting machine in which a web being run is cut at high speed with high accuracy and the length of a piece of cut web can be changed as desired. The term "web" as herein used is intended to mean a relatively long and flexible material which is, in general, 5.mu. to 5 mm in thickness and 10 cm to 3 m in width. These dimensions are only exemplary. The web may be a plastic film of polyvinylchloride, polycarbonate, acrylic nitrile, styrene copolymer, ABS resin, polyester, polyester resin containing glass fibers, or cellulose dielectric. It may also be a sheet of paper or synthetic paper; or a metal foil of aluminum, copper or the like.
Running web cutting machines for cutting a web are in general known in the art. In such a machine, which while the length of the web being run is being measured with a measuring roll, a rotary cutter or a vertically movable cutter driven by a crank mechanism is operated by an electric motor control system. However, such a conventional cutting machine is disadvantageous in the following respects:
(1) In a rotary-cutter having the upper and lower cutting edges arranged in the form of a drum, the cutting edges are positioned through a driving gear. Therefore, it is difficult to obtain clearance and abutting force with high accuracy, and accordingly it is difficult to precisely and sharply cut the web. PA1 (2) In order to sharply cut the web, it is necessary to increase to a certain extent the engagement depth of the cutting edges. This leads to an increase of the diameter of the drum. This is not suitable for short cutting. PA1 (3) With a rotary cutter, the speed of the web in the direction of advancement of the web is changed greatly during the cutting operation. Therefore, it is impossible to precisely and sharply cut the web. PA1 (4) In a method in which the speed and position of the web are detected by the measuring roll, the measuring roll must be brought into contact with the web. This may scratch or cut the web. PA1 (5) When the speed of the web is varied greatly, the cutter cannot follow the speed variations. In this case, it is difficult to precisely and sharply cut the web. PA1 (6) With the rotary cutter or a conventional swinging type cutter, the upper and lower cutting edges engage each other after the web is cut. As a result, the web is liable to move upwards, and therefore the web may be fluttered or scratched. PA1 (7) If a spiral cutting edge is used, the speed of the web may be set to a constant value. However, in this case, it is difficult to manufacture such a cutting edge, and furthermore it is difficult to precisely and sharply cut the web.